Patent Application
20170090438
Not Applicable
Not Applicable
Not Applicable
The disclosed embodiments generally relate to any process that uses fans and pumps to transport air, gas, water, and/or liquid, and more particularly to the fans of air handling units, the pumps of hot and chilled water systems, condensing water systems, water treatment systems, and city water distribution systems.
Many types of buildings require the use of air handling unit (AHUs) systems to supply air at specific temperatures to indoor spaces. Buildings also use chilled water systems to condition rooms at a set temperature but use water as part of the cooling process. Over the years, a variety of configurations and methods for controlling AHUs and chilled and hot water pump systems have been proposed.
Controller 118 receives signals from outdoor air temperature sensor 128, static pressure sensor 130, and flow station 126. It then uses that information to control air handling unit 100. In VAV AHUs (variable air volume air handling units), the set point of the supply air temperature is maintained at 55° F. (the temperature is adjustable, and not limited to that stated herein) using the dampers, heating coils, and cooling coils. Static pressure sensor 130 is installed upstream of the zone dampers and measures the static pressure downstream of the supply air duct. Supply air fan 114 is driven by VFD 112. The supply fan speed is modulated to maintain the static pressure at a constant set point value. VFD 120 controls the speed of return air fan 116 to ensure that the building has a slightly positive pressure.
Although prior art air handling units have been controlled to cool spaces in building interiors, they are not very energy efficient. In particular, prior art air handling units like the one described are controlled to maintain the static pressure set point at a constant value. As a result, the system over-pressurizes the terminal box dampers. In some cases, the static pressure setpoint is reset based on the outdoor air temperature. Since the outdoor air temperature is not representative of all the factors that could influence the static pressure, this reset often ends quite conservatively or leads to occupant comfort related complaints. Notably, in such systems the static pressure sensor is located downstream of the ductwork above the ceiling inside of the building. This thus makes it difficult to find issues and perform maintenance procedures. Another problem is that under partial load conditions, the static pressure is very high. A high static pressure can lead to over-pressurization and cause the terminal box to malfunction. Excessive air leakage in the ductwork and terminal box dampers may also waste energy (by 20%) and increase fan energy consumption by half. In some prior art systems, the fan speed is controlled through pre-selection of the terminal box damper position. However, the problem with this method is that some zones may not attain the same comfort standard as others and it can't be ensured that the preselected zone is is a critical zone.
As shown in the Fig., a plurality of sensors and a flow station is included in the configuration of the chilled water pump system. The pump speed is controlled to maintain the set point of the loop differential pressure. Such prior art pump systems activate and deactivate based on the distribution of water in the pump system. If the loop differential pressure is lower than the setpoint when the pumps are running at full speed, for example, controller 216 activates one or more pumps to provide more water to system 200. When the pump speed is low, the one or more pumps are deactivated. The set point is reset based on the outdoor air temperature or determined according to the prior experiences of the user. It should be noted that since the outdoor air temperature is not the only factor that influences the set point and setting the set point based on knowledge gained through prior experience is not a method that is entirely reliable, the reset in prior art systems tends to be very conservative. The result of this is that the chilled water system consumes more energy.
Additionally, in prior art pump systems such as the one described, the pump working points are often pushed to the position of lowest efficiency as a result of improper pump staging. Thus, even if the design pump efficiency is 75%, in actuality it operates at a low efficiency of 40%. Under partial load conditions, excessive pressure head is often exerted on the cooling coil control valves as well. The pumps consume an excessive amount of energy as a result of the excessive differential pressure set points. As a result, the control valve either gets stuck open or closed (and wastes energy). Otherwise, the control valve must be manually adjusted into position (resulting in extra labor). Prior art systems also tend to have excessively high differential pressure set points that lead to significant pump energy consumption. Finally, prior art systems use differential pressure sensors. These sensors require a lot of maintenance in order to function properly.
In order to solve the issues present in the prior art as well as to increase the energy efficiency of air handling unit and chilled water systems, a novel control system and method is proposed. This control system controls the fan speed of air handling units and the pump speed and staging in chilled water pump systems, thus eliminating the need for the installation of sensors and other system components that are used to help perform these tasks in prior art units.
Accordingly, it is one aspect of an embodiment to improve the energy efficiency of and reduce the costs associated with air handling units and chilled water pump systems. This is accomplished through the addition of a control system that reduces the number of pressure sensors, outdoor air temperatures sensors, flow stations, and static pressure sensors needed.
In one embodiment, a control system for controlling at least one fan or pump and at least one VFD is provided. The control system comprises an input module configured to input a plurality of operating conditions from said vfd and predetermined variables for said system comprising a performance curve, a design flow rate, a design low load flow rate, a design high load flow rate, a VFD current value, a VFD power value, a VFD torque value, and a VFD speed value. The control system also comprises a power module configured to calculate for a measured power value based on the VFD power value, as well as a head, flow rate, and efficiency module configured to calculate for a head value based on the measured power value and the performance curve. It is also configured to calculate for a measured flow rate value based on the VFD current value, VFD power value, VFD torque value, the performance curve, as well as an efficiency value based on the measured flow rate and measured head value.
The control system further comprises a load/unload module configured to stage and modulate a speed of said at least one pump or fan. The control system comprises an identifying step for identifying a working point on the performance curve. It also comprises an activation step for activating the at least one fan or pump when the efficiency value is less than the working point by a predetermined amount and a ratio of the measured head value over a square of the measured flow rate is lower than a ratio of the design head value over a square of the design flow rate. The control system further comprises a deactivation step for deactivating the at least one fan or pump when the efficiency value is less than the working point by a predetermined amount and a ratio of the measured head value over a square of the measured flow rate is greater than a ratio of the design head value over a square of the design flow rate.
Finally, the control system comprises a speed modulation step for controlling a speed of the at least one fan or pump when the measured flow rate is greater than the design high load flow rate so that a ratio of the measured head value over a square of the measured flow rate is equal to a ratio of the design head value over a square of the design flow rate. The control system includes a speed modulation step for controlling a speed of the at least one fan or pump to maintain the low load flow rate when the measured flow rate is less than the low load flow rate. The control system also comprises a speed modulation step for controlling a speed of the at least one fan or pump when the measured flow rate is less than the design high load rate and greater than the design low load rate so that the ratio of the measured head value over a square of the measured flow rate is equal to one plus said design high load flow rate minus said measured flow rate over said design high load flow rate multiplied by a distribution factor and further multiplied by said design head over said design flow rate squared. For clarity, this is shown in equation form as:
In another embodiment, a method of controlling at least one fan or pump to optimize the transport of liquids and/or gases through a system having at least one VFD is proposed. The method comprises interfacing a control device with the system. It further comprises inputting a plurality of system operating conditions comprising a VFD power value, a VFD current value, VFD torque value, and VFD speed value from the variable speed drive into said control device. It also comprises inputting a plurality of operating conditions such as a performance curve, a design flow rate, a design high load flow rate and design low load flow rate into the control device. The method further comprises calculating, by the controller, for a measured power value based on theVFD power value. The method also comprises determining a measured flow rate based on the performance curve, the VFD current value, VFD power value, and VFD torque value.
The method further comprises determining a measured head value based on the measured power value and the performance curve, and determining a design point efficiency based on the measured flow rate and measured head value. The method further comprises identifying a working point efficiency on the performance curve, and activating the at least one fan or pump when the design point efficiency is less than the working point efficiency by a predetermined amount, and a ratio of the measured head value over a square of the measured flow rate is lower than a ratio of the design head value over a square of the design flow rate.
The method further comprises inactivating at least one fan or pump when the design point efficiency is less than the working point efficiency within a predetermined range and a ratio of the measured head value over a square of the measured flow rate is greater than a ratio of the design head value over a square of the design flow rate. The method comprises modulating the fan and pump to maintain the low load flow rate when the measured flow rate is lower than the design low load flow rate. It further comprises modulating a speed of the at least one fan or pump so that a ratio of the measured head value over a square of the measured flow rate is equal to a ratio of the design head value over a square of the design flow rate when the measured flow rate is greater than the design high load flow rate.
Finally, the method comprises modulating a speed of the at least one fan or pump when the measured flow rate is less than the design high load rate and greater than the design low load rate, so that a ratio of the measured head value over a square of the measured flow is equal to one plus the design high load flow minus the measured flow rate over the design high load flow multiplied by a distribution factor and further multiplied by the design head over the design flow rate squared. For clarity, this is shown in equation form as:
In some embodiments the system is an air handling unit while in other embodiments the system is a chilled water pump system having at least one chiller. In embodiments in which the system is a chilled water pump system having at least one chiller, the controller calculates for the design water flow rate and measured head of the at least one chiller.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the following Figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Advantages, features and characteristics of the present disclosure, as well as methods, operation and functions of related elements of structure, and the combination of parts and economies of manufacture, will become apparent upon consideration of the following description and claims with reference to the accompanying drawings, all of which form a part of the specification, wherein like reference numerals designate corresponding parts in the various figures, and wherein:
Before the present methods, systems, and materials are described, it is to be understood that this disclosure is not limited to the particular methodologies, systems and materials described, as these may vary. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope.
It must also be noted that as used herein and in the appended claims, the singular forms “a”, “an,” and “the” include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Although any methods, materials, and devices similar or equivalent to those described herein can be used in the practice or testing of embodiments, the preferred methods, materials, and devices are now described. All publications mentioned herein are incorporated by reference. Nothing herein is to be construed as an admission that the embodiments described herein are not entitled to antedate such disclosure by virtue of prior invention.
In accordance with one embodiment, a sensorless fan and pump speed control air handling unit system is illustrated in
In accordance with another embodiment, a sensorless fan and pump speed control system 400 is illustrated in
Chillers 404 and 406 produce chilled water that is circulated throughout system 400 as well as to valves 414, 416, and 418 and cooling coils 420, 422, and 424 by pumps 410 and 412. When water passes through cooling coils 420, 422, and 424, it is warmed up by the air. The water is then once again redistributed through the pump system in a cyclical manner and is cooled down by chillers 404 and 406. VFDs 408 & 426 control the speed of pumps 410 and 412 to maintain the differential pressure across cooling coils 420, 422, and 424. Control device 302 is configured in communication with VFDs 408 and 426. Said control device controls the manner in which pumps 410 and 412 are staged. It is also configured to control the speed of said pumps. As illustrated in
As shown in
Using the pump performance curve and the current, power, and torque values collected from the VFD(s), Air Flow, Fan Head, and Fan Efficiency Module 506 calculates for an airflow rate when used in system 300. Device 302 calculates for a water flow rate for a chilled water pump system such as system 400 in Water Flow, Pump Head, and Pump Efficiency Module 516 using the same method as in Module 506. Modules 516 and 506 also calculate for the pump head and pump efficiency (in chilled water pump systems) and the fan head and fan efficiency (in air handling units) values, respectively. The fan or pump power values (calculated in modules 504 or 514, respectively) as well as the fan or pump performance curve (fan curve if device 302 is implemented in system 300 and pump curve if implemented in system 400) are used by Modules 506 and 516 to calculate for the fan head and fan efficiency or the pump head and pump efficiency, respectively.
Using the fan head and air flow rates calculated in Module 506 or the pump head and water flow rates calculated in Module 516, AHU Load/Unload Module 508 or Pump System Load/Unload Module 518 identifies the equivalent working points on the fan or pump design curves, respectively. The pump design curve is used if device 302 is implemented in a pump system or the fan design curve is employed if device 302 is implemented in an air handling unit. As shown in steps 510 and 512 of
The control logic of Module 518 follows the same control logic as described for Module 508 [see the prior paragraph] expect that it activates and deactivates pumps rather than fans. Thus, as can be seen in Steps 524, 526 and 528 of
When device 302 is implemented in an air handling unit such as that shown in system 300, Fan Speed Control Module 532 controls the speed of the fan based on a comparison of the measured airflow rate and design airflow rates. As shown in steps 536 and 538 of
When device 302 is implemented in a pump system such as system 400 as shown in
While the method in which device 302 controls the pumps of chilled water pump systems and the fans of air handling units is similar, device 302 makes an additional calculation before solving for the pump speed ratio when implemented in chilled water pump systems like that shown in
Various features and advantages of the invention are set forth in the following claims.
